Questions from students

My physics class has come up with some questions lately that I
haven't been able to find answers to. If some of you could help, I
would appreciate it.

1. What causes fluorescent bulbs to "burn out"?

2. If you cancel out a repetetive sound with and "inverse sound"
that is generated by some of the new sound cancelling devices that
are on the market now, what happens to the energy in the original
sound and in the inverse sound?